Process for the production of alumina from aluminum nitrates



Dec. 6,1927. 1,652,119

1 5. F. HALVORSEN ET AL PRocEss FQR THE PRODUCTION OF ALUMINA FROMALUMINUM NITRATES Filed May 2 1924 I rotatory furnace to such gas IPatented Dec. 6, 1921.

uNiTso sTAr sfPATEN T OFFICE.

BIRGER-FJELD fnanvonsnn, or osLo, HANS :roncnnu FALCK, or NOTODDEN, AND1 osrs'rmn navimn, or osLo, NORWAY, ASSIGNORS 'ro NORSK nxnnonnnx'rmsxxvantsroraxrmsnnsxaa, or osLo, NORWAY.

r'nocnss FOR THE rnonu-c'r'roiw oranummarnom ALUMINUM NITBATES.

- Application filed ma 28', 1924, Serial No. 716,498, imam Norway June1a, 1928.

The production 'of alumina from aluminum nitrate canjbe effected eitherby precipitatingaluminum. hydroxide withfbases or by heating thenitrate,for instance, in a comes decomposed, whereby .the-nitric acid is setfree and the aluminum oxide is kept back. There are several drawbacksattached to the latter process,'for 'instance, fritting,'

which causes the obstruction of the apparatus.

Thisdrawback is av0ided, however, in the method that consists ofdecomposing the aluminum nitrate-in a melted solution of alkalinenitrates. But this process. has a diiierentdrawback, that is,'thata.,comparatively large. quantity of alkaline nitrate circulates in theapparatus:

'In the present invention the' addition of alkaline nitrates is avoidedand, in addition,

the reaction-mass does 'not melt or become caked, neither does-theapparatus become Obvstructed. g

The process consists of the nitrate being converted into, spray in awarmcurrent of and the aluminum nitrate being decom posed into alumina andnitric acid or nitrous gases, respectively. "It can, for instance, beeffected bymeltin'g the aluminum nitrate in its crystal waterandconverting the melted solution into spray n a chamber that ispervaded' by warm gases. Ifon'e has an aluminum nitrate that smixed withanothennitrate, forinstance, potassium or calcium nitrate, thismixturemelts very easily in 'its crystal water and can be'treated aspure nitrateof aluminum as long as care is taken that the temperature isnot so high that 'aluminate is formed. The temperature of .the gaseswhen they enter the chamber may be very high, for instance 1000*,without this having a bad efiect on the reaction products, because thetemperature of the separate particles is-limited'by the process ofdecomposition which consumes heat, so that during the relatively shorttime they are in contact with the gases,

their temperature does not exceed that of decomposition,

which should not'be more than 400. vBesides, the tem-' perature mayeasily' be regulated either by the quantity of the melted mass or byregua degree that it .be-

lation of the current-of gas. If one has a basic nitrate of aluminum,these materials can, even if it .is diflicult to liquefythem,

still be treated to advantage by the present process, as the materialscan be placed in the decomposing chamber in the form of I powder. a Inorder that the particles shall be in contact. with the warm. gases for asufiicient space of time it is possible,if it is notdesirable to makethe chamber more than a certain length, that an arrangement may be madeso that the current of gas be tangential and whereby the mass will becaused to lengthening the time during which the ma- Ifollow the currentof gas. Another way of kind of packing material. The introductionof thematerial to'be' calcined, either in the form of a solution or a powder,can be effected bynozzles or by screws, or it can be converted into dustby compressed air or by other gases.

.- The most simple form-for the chamber is Y .that or a tower thesection of which is theshape of. a circle. Y

The aluminum oxide or hydroxide is deposited either in .the decomposinchamber itself or inan annexed dust cham er which may be provided with adevice for the precipitation of dust. The gases which contain nitricacid and nitrous gases are, when cooled, introduced into an absorptionapparatus of the kind for the absorption of nitrous gases.

A reaction chamber may also be used into which the hot. current of airis conducted tangentially so that it moves in the chamber spirally andescapes through a tube thatis in the middle of the top of the chamber.The melted or heated aluminum'nitrate is introduced onto a. rotatorydisc in or near the axle of the apparatus and is thereby thrown in theform of spray through the hot current of air, whereby it becomescalcined and falls down into the lower part of the apparatus or itsticks to the sides of the apparatus.

The attached drawing shows an example of such a reaction chamber havinga conical bottom. I

Fig. 1 is a vertical section of the apparatus with parts appearing inelevation; and Fig. 2 is a horizontal section through the reactionchamber.

Referring to the drawing A is the tube whereby the hot air enters... Themelted nitrate enters through tube B andfalls down onto the rotatoryatomizing disc C. The aluminum oxide that has stuck to the Walls is nowand then removed by means of the ring D, and is collected in a funneland taken out through tube E. vThe gas passes out through tube F. v

The reaction chamber ought to be well insulated against loss of heat andshould be lined inside with fireproof brick.

The following may be given as an example of how the method may beeffected -A mixture of 20 per cent KNO and Y80 per cent A1,,(NO 1'8H Ois heated to 70 0. whereby it melts in the crystal water and isconducted onto the atomizing disc.

aratus, 3 metres in diameter, is suitable or an amount ofsalt of 500kilo rammes per hour and 1400 kilogrammes 0 hot air per hour can beblown into the apparatus at a temperature of 1000 C.

Instead of air heating. gases may be-"usedor hot nitrous gases from theelectric furnace, or other hot gases.

We claim: 1. Process for the production of alumina from aluminumnitrates comprising heating the nitrate, converting it into spray and'conducting it into a chamber pervaded by hot gases;

.2. Process for the production of-alumina from aluminum nitratescomprising heating the nitrate, converting it into spray and conducting1t into a chamber into which hot chamber, and subjecting the suspensionto the action of hot gases until'th'e decomposition. of the aluminumnitrate is effected. In testimony whereof, we afiix our signatures. 1

' BIRGER FJELD HALVORSEN;

HANS J OAOHIM FALCK. @YSTEIN RAVNER,

